The present invention relates to a system for detecting troubles in an intake system of an automotive engine.
A fuel injection system, in which a basic fuel injection quantity is determined in accordance with pressure in an intake pipe and speed of the engine, is used for automobiles. In such a system, if trouble occurs in the intake pipe, such as a blind cap comming out on the intake system downstream of a throttle valve caused by backfiring of the engine, the air is induced in the intake pipe passing through a hole for the blind cap without passing through the throttle valve. The pressure in the intake pipe rises with the induced air. As a result, the fuel injection system operates so as to increase the basic fuel injection quantity in accordance with the high intake pipe pressure, which causes an abnormal increase of the speed of the engine regardless of the intention of the driver.
Japanese Patent Application Laid-Open No. 58-214632 discloses a system for solving such a problem. The system stores reference data of intake pipe pressure determined by the opening degree of the throttle valve and the engine speed. Detected intake pipe pressure is compared with a stored reference pressure. If the detected pressure is higher than the reference pressure, the basic fuel injection quantity is fixed to a predetermined value, thereby preventing an abnormal increase in the engine speed.
However, in the system, when an abnormally large amount of intake air flows in the intake passage, the air-fuel mixture becomes lean, because the basic fuel injection quantity is set at the predetermined value. If the mixture becomes extremely lean, misfiring of the engine occurs. Frequent misfiring cause an abnormal rise in the temperature of the exhaust gas which can break the exhaust system and a catalytic converter in the exhaust pipe.